Spin correlations in the two-dimensionalS=1Heisenberg antiferromagnet

Abstract

${\mathrm{K}}_2$ ${\mathrm{NiF}}_4$ is a well-characterized planar antiferromagnet that represents a good approximation to the idealized two-dimensional (2D) S=1 Heisenberg antiferromagnet. In 1970, Birgeneau, Skalyo, and Shirane measured the 2D antiferromagnetic structure factor in ${\mathrm{K}}_2$ ${\mathrm{NiF}}_4$ over a wide range of temperatures. In this report we compare their experimental results with the predictions of a recent theory for the 2D quantum Heisenberg antiferromagnet by Chakravarty, Halperin, and Nelson. The theory describes the temperature dependence of both the absolute value of the correlation length and the relative structure factor peak intensity quantitatively. The crossover temperature to 2D Ising critical behavior is also properly predicted.